Thermoplastic/thermoset composite systems are being employed in an increasing number of applications including piping, high pressure gas cylinders, and chemical storage tanks. For these applications, articles are formed from the thermoplastic by extrusion, blow molding, rotomolding, or some other conventional melt processing technique. In a second step, the thermoplastic is wrapped or coated with the thermoset material. Typically, the thermoset is also a composite system containing glass or carbon fibers. The result is a composite structure which can be readily fabricated into a wide variety of shapes and sizes, yet exhibits high strength in combination with the intrinsic properties of the thermoplastic substrate (i.e., impact, chemical and stress crack propagation resistance).
One of the critical design parameters which govern the ultimate properties of the thermoplastic/thermoset composite structure is the strength of the interface between the thermoplastic and thermoset. Strong interfacial bonds have the desirable characteristic of evenly distributing and transferring stress from the thermoplastic to the high modulus thermoset composite. Thus, strong interfacial bonds increase the service pressures and longevity of fabricated parts. It is preferred that the bond be formed at temperatures which do not melt or distort the existing thermoplastic part.
Polyketone polymers are expected to have good compatibility with thermoplastic/thermoset systems such as epoxies. This is particularly true when the epoxy systems are cured with amine curing agents. Polyketone polymers are known to react with primary amine functionalities at temperatures well below the melting point of the polyketone polymer. By using conventional curing conditions around (150.degree. to 180.degree. C.), a primary amine cured epoxy is expected to readily form covalent bonds with the polyketone substrate. It is known that due to steric hinderance, some amine curing agents will more readily bond to polyketone polymers than others.
As previously disclosed, the interfacial strength between the components of a composite system defines the ultimate properties which can be achieved. Yet when applying epoxy systems to a solid polyketone polymer substrate using conventional curing conditions, the interfacial bond is frequently insufficient to achieve the desired mechanical properties of the composite. While many of the curing agents for epoxy systems are capable of covalently bonding to the polyketone substrate, bonding does not occur due to the competitive reactions with the epoxy systems and the attendant decrease in molecular mobility.
However, because of its desirable mechanical, barrier, and chemical resistance properties in combination with the expected bonding propensity, polyketone polymer is a highly desirable material for use in thermoplastic/thermoset composite systems.